1. Field of the Invention
The present invention relates to a method for vapor deposition of silicon on substrates to impart properties for use in corrosive and vacuum environments. More particularly, the present invention relates to an improved method of applying a silicon passivation layer to the surfaces of substrates.
2. Brief Description of the Related Art
The present invention overcomes many known deficiencies by using silicon as a passivation layer for a variety of substrates, including those comprised of metal (ferrous and non-ferrous), glass, carbon, copper, quartz, nickel-containing ferrous alloys, titanium, aluminum and ceramics. Substrates comprised of these materials generally have been known to have undesirable properties, which may, for example include one or more of the following: chemisorption of other molecules; reversible and irreversible physisorption of other molecules; catalytic activity with other molecules; allowing of attack from foreign species, resulting in a molecular, structural and/or cosmetic breakdown of the substrate surfaces and/or bulk; offgassing or outgassing of volatile materials (e.g. water vapor and organics), diffusion or permeation or other processes resulting in the release of gas molecules from a substrate into a vacuum environment resulting in extensive time required to reach a target vacuum and/or the inability to achieve a target vacuum and/or the inability to maintain a target vacuum; hydrogen permeation of a substrate where the is inner portion is subjected to vacuum.
Previous art has focused on layers of silicon modified by oxidation to prevent adsorption. Other previous art has looked at the use of silanes or silicon hydrides passed over metal surfaces at low temperatures to passivate the metal surface.
This invention has utility for substrates which may come in contact with species which degrade, are adsorbed or attack metal surfaces (such as organo-sulfurs, hydrogen sulfide, alcohols, acetates, metal hydrides, hydrochloric acid, nitric acid, sulfuric acid).
The prior art has utilized a single treatment of silicon hydride gases, either for silicon deposition or adsorption to metal surfaces, to impart passivation. This invention utilizes singular and multiple treatments with the silicon hydride gases to impart desired passivation by deposition of silicon.
Prior art also indicates preparation of metals surfaces by exposure to reducing gases prior to silicon deposition. This invention does not utilize such a pretreatment to achieve a passive surface.
U.S. Pat. No. 4,579,752 issued on Apr. 1, 1986 to Lawrence A. Dubois, et al. for an “Enhanced Corrosion Resistance of Metal Surfaces” discloses a method to increase the anti-corrosive characteristics of metal surfaces by creating a protective surface coating with silane gas in the presence of an oxidizing agent to produce a protective layer of SiO and excludes the use of iron in a substrate.
The present invention does not employ an oxidizing agent and therefore generates a layer of amorphous silicon. Additionally, the present invention has the ability to treat substrates with iron content in addition to those with non-metallic composition (e.g. carbon, silicon).
U.S. Pat. No. 4,671,997 issued on Jun. 9, 1987 to Francis S. Galasso, et al. for “Gas Turbine Composite Parts” utilizes multiple layers of silicon carbide (SiC) and silicon nitride (SiN) on gas turbine engine environments. The protective coatings are deposited at high temperature with organochlorosilanes as the reactive precursor.
U.S. Pat. No. 4,714,632 issued on Dec. 22, 1987 to Alejandro L. Cabrera discloses a “Method of Producing Silicon Diffusion Coatings on Metal Articles” where a silicon diffusion coating is formed on metal objects by first preheating in a reducing atmosphere.
U.S. Pat. No. 4,173,661 issued on Nov. 6, 1979 to Bernard Bourdon for a “Method for Depositing Thin Layers of Materials by Decomposing a Gas to Yield a Plasma” discloses a method for depositing thin layers of materials in the manufacture of silicon semi-conductor devices by applying a high-frequency, alternating voltage between a conductive earth surface and a conductive target surface located on opposite sides of a substrate to form a plasma in a chamber in the vicinity of the substrate.
U.S. Pat. No. 5,299,731 issued on Apr. 5, 1994 to A. Nimal Liyanage et al. for a “Corrosion Resistant Welding of Stainless Steel” discloses a process for welding stainless steel tubing in the presence of an inert gas having a silicon base gas in particular SiH4. The stainless steel welding process of the '731 patent discloses utilization of a silicon containing gas, with argon for a purge.
U.S. Pat. No. 5,480,677 issued on Jan. 2, 1996 to Yao-En Li et al. for a “Process for Passivating Metal Surfaces to Enhance the Stability of Gaseous Hydride Mixtures at Low Concentration in Contact Therewith” discloses the use of temperatures of less than the passivating agent gaseous hydride decomposition temperature, and uses silane and other gaseous hydrides in their original form (molecular structure) to adsorb to a metal surface.
U.S. Pat. No. 6,511,760 issued on Jan. 28, 2003 to Gary A. Barone et al. discloses a method for passivating the interior surface of a gas storage vessel where silicon deposition is controlled to apply one or more layers of silicon to the interior surface of a vessel under pressure and heat.